Many devices include non-linear elements, such as power amplifiers. These elements produce output signals from input signals in accordance with non-linear relationships.
Often, specific performance requirements do not accommodate such non-linear relationships. For instance, wireless communications standards, (e.g., GSM/EDGE, WCDMA, and so forth) call for strict spectral requirements to be met. In order to meet such requirements, devices must preserve waveform quality at various power levels.
Thus, techniques are often needed to mitigate non-linearities so that output signals are produced in accordance with more linear relationships. However, a tradeoff often exists between reducing non-linearities and providing efficiency. More particularly, some non-linear devices operate more efficiently when the output response is non-linear. For example, a power amplifier may become increasingly efficient as its operation approaches saturation.
Correction techniques can be employed to compensate for non-linearities. Such techniques typically involve a preliminary stage that precedes a non-linear element. The preliminary stage creates a “pre-distorted” input signal that is sent to the non-linear element. As a result, the preliminary stage and non-linear element may, in cascade, operate in a substantially linear manner.
Accordingly, techniques are needed to determine characteristics for pre-distortion operations.